The present invention relates to the field of data transport in a communications system; more particularly, the present invention relates to a backplane protocol to enable transport of time-division multiplexed data and block data (e.g., packet, cell, etc.) between cards in a telecommunications system.
Data traffic can be categorized into two types: packet and time-division-multiplexed (TDM). TDM data requires deterministic transport and requires low delay. Packet data may require these characteristics as well, but in other instances can tolerate delay. The main difference between the way systems handle TDM data and packet data is that TDM bandwidth is reserved regardless of the presence of data, while packet data only requires bandwidth if a packet is present. If one packet is not present another packet can use the bandwidth.
In many current telecommunication systems, both TDM data and packet data are often transferred between line cards. The line cards are coupled together using one or more interconnects or switch fabrics. Such existing systems require the addition of an additional interconnect and/or separate switch fabrics to accommodate both packet and TDM data traffic. Providing separate data paths to each type of traffic requires additional expense. The additional expense is doubled if redundant fabrics are required for fault protection, which is typically necessary in prior art systems.
Switches typically require some sort of control channel between elements within the switch. These communication channels are used in the inner workings of the switch and are usually transparent to the user. Many prior art systems require control channels that are managed and provisioned separately. This implies that extra backplane, hardware, and software resources are needed, thereby requiring higher system cost and power.
Packet switches usually require that packets be broken up into smaller blocks as they pass through the switch fabric. These blocks are typically of a fixed size. This results in throughput inefficiencies for packets which are slightly larger than a multiple of this fixed block size. To avoid this problem of throughput inefficiencies, prior art systems run the switch fabric at up to twice the required speed. This results in wasted bandwidth, higher power, and cost.
A typical centralized, switch fabric approach also makes incremental protocol upgrade difficult since all traffic passes through a central point. Any protocol change must take into account the limitations of this central fabric. A protocol upgrade in such systems often requires a change-out of all cards in the system.
When backplanes are used, the links in the backplane are clocked using a timing reference. Prior art systems might use the network reference for the backplane links. This makes it hard to implement more than one timing domain in a network box, and it also requires more complicated timing logic for changing references.
A method and apparatus for transferring information in a communications system is described. In one embodiment, the method comprises creating a frame of information on a first line card and sending the frame over a backplane to a second line card using a serial link interconnect. The frame comprises first, second and third portions. The first portion includes information to process the second and third portions. The second portion has packet and time-division multiplexed (TDM) data in multiple channels. Each of the channels is allocable to packet data or TDM data. The third portion includes data placed into the frame to accommodate for differences in timing references between the line cards.